Alternating-current electrical instrument of the moving-coil type.



R. D. GiFFORD. ALTERNATING CURRENT ELECTRICAL INSTRUMENT OF THE MOVING COIL TYPE.

APPLICATION FILED IAN- I81 l9l5.

7h 1 9 1 1L 2 .Umu u A d m n e t a P //V VE/V TOR v WIT 5535s.-

RANDOLPH DOUGLAS, eIEEoE or cnINe onD, ENGLAND, AssIeNon '10 Mnssns.

NnLDEn BEo'rnEns & 'rHoMrso LIMITED, or LONDON, ENGLAND, A conronn- TIoN or ENGLA D.

ALrEnNATINe-cUnnENr ELECTRICAL INSTRUMENT or THE MovINe-con. TYPE.

Specification of Letters Patent.

Patented Au 21,1917.

Application filed January 18, 1915. Serial No. 2,907.

of or includes a conductor traversed by an alternating currentor a rectified alternating current or a varymg or interrupted cont1n-.

uous current) such for example as ammeters,

voltmeters, wattmeters, phase indicators, synchronizers, and the like. In such instruments current is usuallyled to the moving active element by means of metallic conductors, a method which has several drawbacks among which is the fact that the moving activeelement is controlled and re stricted. Or the current has been introduced by brushes which has the drawback that friction is introduced. Or the current has been introduced by induction but in such away that an action is set up between the circuits carrying inducing and induced currents respectively tending to produce move-' My invention is designed to obviate these I drawbacks and it consists in connecting the moving active element of the instrument materially with the secondary winding of a.

transformer having nomechanical connection with its iron circuit or the primary winding thereof, no action'being set up between the inducing and induced circuits which will tend to produce or restrain movement.

In order that my invention may be readily understood I shall now proceed to describe by way of a type or example one form thereof and to aid such description I append hereto a sheet of drawings which diagrammatically illustrate the principle of my invention. i

In the said drawings Figure I is a part section, part elevation and Fig. II a plan.

The straight line 1 represents the angularly moving spindle of the instrument and upon it I mount the disk 2 (preferably of non conducting material) and at the edge of this disk I place a circular coil of wire 3 concentric with the spindle 1 and the ends 4, 5 of which coil are connected with the moving active element 6 of the instrument. The insulating disk passes without touching through a small gap 7 in the iron circuit 8 of a small transformer of which the coil 3 forms the secondary. The iron circuit is provided at another part with a primary winding 9. The circular coil being concentric with the spindle of the instrument it can rotate with the latter (through more than a complete revolution if so desired) without in any way changing its position relatively to the magnetic circuit of the transformer. Consequently in so far as the currents flowing in the primary and the secondary are concerned, there is no tendency to rotate the spindle in either one direction or the other, or to hold it in any one position. In other words the transformer will not in any way affect the movement of the spindle caused by the moving active element.

It will be understood that the present invention is not limited to the typical form thereof described. Thus a secondary coil of some shape other than circular might be em ployed provided that the magnetic circuit is such that the departure from circularity does not cause any turning moment in the secondary coil of the transformer. Further, I may employ a transformer in which there is no iron circuit but in which the mag netic circuit is of air for example.

By the present invention the current which it is desired to introduce into the moving active element is brought in without any control or restriction or friction, or inductive effect tending to produce movement.

It will be seen that by means of my inven vtion as hereinbefore described a current may be introduced into the moving activeelement by variations or interruptions in the strength of a continuous current flowing in the primary of the transformer.

I use the term iron circuit in its generic sense and not as implying that the magnetic circuit which it constitutes is made of the metal iron.

It is obvious that my invention is applicable to polyphase as well as to monophase work. a

It will be understood that it is not necessary to support the secondary coil upon a Copies of this patentmay be obtained for disk. It might be supported for example on a spider or even a single bar placed diametrically with respect to the secondary coil. i

It is to be noted that my invention involves no mechanical obstacle (such as conducting wires or other parts) to free rotation of the spindle and its attached parts.

Myinventi'on is particularly useful in the case of power factor meters.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is 1. In an alternating current electrical measuring instrument of the moving coil type, the combination with the moving active element of the said instrument, of a transformer thesecondary of which is mechanically connected with-the said moving active element but is mechanically discon- "'nected from its primary, the arrangement being 'such that no torque is set up between the primary and secondary members whlch will tend to produce or to restrain movement, substantially as described. I 2. In an alternating current electrical measuring instrument of the moving coil type, the combination with the moving active element of said instrument, of a transformer, the secondary of which is circular in shape and is mounted on a shaft connected with said moving active element, but is mechanically disconnected from its primary and rotates within the air gap of said primary, the arrangement being such that no torque is set up between the primary and secondary members, substantially as described.

In witness whereof I have signed my name to this specification in the presence of two subscribing witnesses.

RANDOLPH DOUGLAS en ronn.

Witnesses O. J. VVonTn, A. NUTTING.

five cents each, by addressing the Commissioner of Patents, Washington, D. C. i 

